1. Field of the Invention
The present invention relates to an optical apparatus such as a lens apparatus, a digital camera, or a video camera.
2. Related Background Art
In many of the optical apparatuses such as those described above, a so-called rear focus (inner focus) zoom lens is used. This rear focus zoom lens includes: a front lens that is arranged on a most object side, a zoom lens that moves in an optical axis direction on an image surface side than the front lens and performs zooming operation; and a focus lens that moves in the optical axis direction and performs correction (compensator function) for image surface fluctuation due to the zooming operation and focusing.
In the rear focus zoom lens described above, the focus lens is driven by a focus drive signal from a camera controller, whereby focus adjustment is performed. In addition, the zoom lens is driven by a zoom drive signal, which is generated by an operation of a zoom switch by a user, and the focus lens is also driven by the zoom drive signal to correct image surface fluctuation due to zooming operation, whereby zooming is performed.
An optical apparatus has been proposed which makes it possible to perform focus adjustment and a zoom operation manually using a focus operation ring and a zoom operation ring as well in order to improve operability (e.g., paragraphs 0022 to 0028, FIG. 1, etc. of Japanese Patent Application Laid-Open No. H09-304679).
FIG. 7 shows a structure of a lens apparatus mounted with a conventional rear focus zoom lens. In FIG. 7, a manual focus ring 101a and a manual zoom ring 101b, which perform a focus operation and a zoom operation manually, are elements constituting an exterior of the lens apparatus. The manual focus ring 101a and the manual zoom ring 101b are held by an external unit 101 so as to be rotatable. Note that, the external unit 101 also includes electric components such as sensors for detecting rotation of the manual focus ring 101a and the manual zoom ring 101b and an actuator for driving a focus lens and a zoom lens, which are not shown in the figure, on the basis of outputs from the sensors as well as the manual focus ring 101a and the manual zoom ring 101b. 
As described above, the components of the external unit are constituted as a unit and then attached to a lens barrel unit to be described later, whereby the lens apparatus can be assembled easily compared with the case where respective components are attached individually.
Reference numeral 102 denotes a lens barrel unit in which optical elements such as a front lens, a zoom lens, and a focus lens are held or housed so as to be movable in an optical axis direction.
A tubular section (hereinafter referred to as a front holding barrel) 103 on an object side (an inner side in the figure) of the lens barrel unit 102 is inserted into the inside of the external unit 101 from an image surface side (a rear side in the figure). Then, the external unit is assembled around an outer periphery of the front holding barrel 103. Therefore, an inner diameter 101c of the external unit 101 is set larger than an outer diameter 103b of the front holding barrel 103. Note that the outer diameter 103b of the front holding barrel 103 is determined according to an outer diameter of the largest front lens among lenses.
Reference numerals 103a and 104a denote flange sections that are formed at an end on the image surface side of the front holding barrel 103 and at an end on the object side in an image pickup element holding barrel 104 constituting a part on the image surface side of the lens barrel unit 102, respectively. The front holding barrel 103 and the image pickup element holding barrel 104 are combined in those flange sections 103a and 104a. Note that an image pickup element, which photoelectrically converts an object image focused by the rear focus zoom lens, a lens stop unit, and the like are held in the image pickup element holding barrel 104.
Here, both the flange sections 103a and 104a have to be formed such that a space for combining the flange sections 103a and 104a is secured while a space for arranging an actuator, which drives the lenses and the lens stop unit arranged in the image pickup element holding barrel 104, is secured. Consequently, each of the flange sections 103a and 104a has an extremely large outer diameter compared with the outer diameter 103b of the front holding barrel 103 and has the largest outer diameter in the lens barrel unit 102.
Therefore, when the external unit 101 is assembled to the lens barrel unit 102, it is necessary to insert the front holding barrel 103 of the lens barrel unit 102 into the inside of the external unit 101 from the image surface (image pickup element) side.
Incidentally, recently, more wider angle of a zoom lens has been desired in many cases, and a wide-angle zoom lens tends to have a larger diameter (outer diameter) of a front lens. Consequently, the outer diameter of the front holding barrel 103 in FIG. 7 also increases.
However, in the structure of the conventional lens apparatus described above, as the diameter of the front lens (i.e., the outer diameter of the front holding barrel 103) increases, it is necessary to increase the inner diameter of the external unit 101 to make it possible to insert the front holding barrel 103 into the inside of the external unit 101. On the other hand, since sizes of electric components to be arranged in the external unit 101 are fixed, it is difficult to reduce a difference of outer and inner diameters necessary for the external unit 101. This results in an increase in size of the outer diameter of the external unit.